1. Field of the Invention
The present invention relates to a method wherein a bar code imprinted into a product is read using a reader device in order to transfer forward a signal formed by said code. The invention also relates to a reader device wherein the inventive method is used. The invention further relates to the use of said reader device and said method.
2. Prior Art
At present bar codes are made onto products using, for instance, printing ink, in which case the reading of the bar code is based on a method wherein reflective differences are detected. In a bar code reader pen there is a light source and a receiver which detects the dark and light areas of the bar code as the reader pen is transported over said bar code. An analog signal is formed, which is transformed into a digital signal for the actual reader device. In a scanner type reader there is one or several light sources and one or several receivers which read the bar code when the reader device is kept in position over said bar code.
The barcode bars are distinguished from each other based on the fact that dark and light areas reflect light differently. Thus, a correct reading of a code usually requires that the reflection from light areas is at least four times stronger than the reflection from dark areas, or, contrarily, the reflections from dark areas must, correspondingly, not exceed 25% of the reflections from light areas.
On the other hand, a method (see Finnish patent No 85956) has been developed for making a bar code in the surface of a product, wherein a sticker comprising a stamp means in accordance with the bar code is placed on the surface of the product. When the sticker is pressed against the product, the bar code on the sticker will form a depressed permanent bar code into the Surface of the product. In this code the original reflection both from the background and from a bar is essentially equal, and this bar code cannot be read with usual bar code readers before the depressed portions have been painted for example black.
Arrangements are prior known for reading especially the embossed writing used in connection with credit cards or the like. Thus, GB patent publication No. 1 470 562 discloses an identifying arrangement wherein the portions rising above the base plane of a surface are identified in such a manner that light from a lamp is brought to pass through a plate comprising two slots. Said plate is parallel to the surface of the object and is located at a distance therefrom. The distance between said slots is arranged such that a light beam passing inclined through the first of said slots will meet a lower surface, and will be reflected at a corresponding inclination via the second one of said slots out to a receiver. On the other hand, if the light beam meets a surface located higher up, the lateral displacement of the beam will be so short that the light beam will not meet the second slot and thus it cannot reach the receiver. In such an arrangement the internal relative measures in the apparatus are extremely critical and only embossments fulfilling certain criteria can, at each arrangement, reflect the light in such a manner that the desired detection is obtained.
U.S. Pat. No. 3,947,691 also describes a reader device for embossed printing in credit cards, said device comprising light emitting first optical fiber means and receiving second optical fiber means located at a distance therefrom. In the device according to said patent an optical fiber is arranged perpendicularly against the marked surface of a body, for illuminating a portion of said surface. Correspondingly, receiving means are located perpendicularly against said surface. The construction is technically rather complicated and its precision is widely depending on how small the optical fiber arrangement is built, and with the use of said apparatus it is mainly possible to exactly observe only markings located in a distinct area, the width of each marking further being of a certain dimension. Thus, the use of said known arrangement for the general reading of bar codes is difficult i.a. because it is normally impossible to position the bar code reader exactly.
GB patent publication No. 1 359 254 also discloses an optical card reader wherein the end of a light bringing optical fiber and, correspondingly, the end of a light determining optical fiber are arranged into the immediate vicinity, or in practice, into contact with the surface of said card. Said optical fibers are located at a certain mutual angle. In this application too a complicated optical fiber optics is utilized. In U.S. Pat. No. 4,020,327 there is, on the other hand, a general comment regarding the general inapplicability of optical fiber optics, and an optical arrangement is disclosed instead which comprises several light sources and one receiver, wherein the apparatus is based on a rather complicated optical arrangement for focusing several light beams onto certain areas of the object to be read, and further for focusing reflected beams from these areas to a common receiving point. The solution disclosed in this document is also technically complicated and demands great exactness of the optical arrangements and on the mutual dimensional relations between the components related thereto.